I had recently made some measurements of RTTY and PSK31 which shows that sound card driven programs using DATA-A can put out a cleaner transmitted signal than the K3's internal generators in the PSK-D and FSK-D modes.
Unlike many other rigs, the K3 is very forgiving about the precise Mic Gain/audio levels. I'd found that with Mic Gain set to 6, audio levels anywhere between 250 mV RMS and 350 mV RMS work equally well, with the RF output tracking the PWR knob setting and not needing to readjust the audio levels. With many rigs, you need to adjust the RF output through the amount of audio drive, just so you can keep the ALC turned off. With the "ease of use," together with lower IMD, there are few reasons to use PSK-D (or FSK-D, unless you are out in the boonies with just a Morse paddle) on the K3. I've just spent a little time this morning and compiled the results into a web page here: http://homepage.mac.com/chen/Technical/K3/Digital/digital.html The write up includes cases where I found a power creep (with an attendant ALC creep and worsening IMD numbers from PSK31). It appears that the power creep could be the result of insufficient audio drive. With the "good" fixed audio level mentioned above, I see no power creep at various RF power settings. The measurements also show that the K3's transmit IMD is low enough that AFSK RTTY waveshaping by software can help reduce the keying sidebands when compared to a rig (K3 or otherwise) that uses FSK. The bottom line (if you want to skip the nitty gritty details in the above web page) is that the K3's PA at 50 watts average PSK31 power is capable of better than -35 dBc IMD for close spaced carrier pairs. By carefully tuning the audio drive, I can get -37 dBc, so I assume the PA itself is good to at least that. The -35 dBc number is probably limited by something else in the chain. 73 Chen, W7AY ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
